Roaming Pokémon

As opposed to the stationary Set Encounters, Roaming Pokémon wander around the whole region and are found anywhere in the wild with an extremely slim chance. This encountering method is exclusive to Legendary and Mythical Pokémon, as well as 2 Event Pokémon, currently.

Mechanics
In core series games, Roaming Pokémon had 2 notorious habits: they would constantly teleport from route to route and immediately try to flee when encountered, keeping their health and status conditions if they are damaged before successfully retreating. However, in Pokémon Brick Bronze, regular Roaming Pokémon instead have an encounter rate of 1/1000 (0.1%) generally in all locations with grass and flower patches, as well as walking encounters including caves which, in main series games, hardly allowed Roaming Pokémon to show up. They will also battle the player instead of attempting to escape in the first turn, in sharp contrast to their behaviour in the core series. As of now, all regular Roaming Pokémon appear at Lv. 40, while the levels of event Roaming Pokémon are not fixed.

Roaming Pokémon are also no longer "One chance only" — if the player is very lucky, he or she can encounter the same Roaming Pokémon multiple times, even if it is already captured, and beating Roria League is not required to make Roaming Pokémon show up again if any of them is defeated. As a result of this change, status conditions no longer remain on Roaming Pokémon if the player fails to catch them. Nevertheless, with the general rarity being 0.1% and specific encounter rate further divided, players are still strongly recommended to save immediately after successfully catching a Roaming Pokémon. Saving before searching for one is also recommended to preserve Poké Balls, in case the attempt of capturing ends up as a failure.

Game Pass and Ro-Power
From the Aredia City update on 20th January, 2017 onwards, a Ro-Power of quadrupling the Roaming Pokémon encounter rate is introduced. Its selling price is 150 Robux — the priciest among all Ro-Powers. It only lasts for 1 hour per each purchase and is only available if 3 or more Roaming Pokémon encounters are enabled.

A game pass for doubling the chance for Roaming Pokémon to show up is also added. It is very expensive and costs 600 Robux — quadruple of the marked price for the afore-mentioned Ro-Power, but the effect is permanent. These 2 boosts can stack with each other, bringing the maximum encounter rate to 1/125 (0.8%); sadly, they do not work on Event Roaming Pokémon.

Master Balls?
Master Balls can also be bought in Poké Ball Emporium, Anthian City - Shopping District starting from Aredia City update. Being the ultimate Poké Ball, Master Ball is guaranteed to catch any Wild Pokémon, and for the first time in any Pokémon games, it is available for purchase. Each Master Ball costs 50 Robux and cannot be purchased in bulk, disabling the Premier Ball bonus.

For players who do not have enough Robux, they can buy Quick Balls and use them immediately when a Roaming Pokémon shows up because Quick Balls have 5× catch rate in the first turn. In case Quick Balls fail, when players are battling Roaming Pokémon overnight or in caves, Dusk Balls are the best option with the 3.5× catch rate. Elemental Balls are also good back-ups, using the Roaming Pokémon's type to players' advantage, but they cost double the price of Quick and Dusk Balls, while only having the catch rate as a maximum effect Dusk Ball.

Weaken + Status Condition
As Roaming Pokémon here no longer flee on the first turn, players can simply apply the same strategy for catching Set Encounter Legendary or Mythical Pokémon. Start by throwing a Quick Ball, which has 5× catch rate in the first turn. If it fails, weaken the Pokémon with attacks that should not be able to make it faint, until its health bar is in red. False Swipe is a commonly used attack for catching Legendary and Mythical Pokémon because it is a unique attack that will never render the opponent unable to battle. TM54 False Swipe is available for purchase in the BP Shop, Colosseum Marketplace for 45 BP, while some Pokémon also learn this move via levelling up.

Inflicting a status condition also increases the catch rate, but players are strongly discouraged from burning or poisoning the Pokémon in order to prevent knockouts. Once the Pokémon is in critical health and is asleep, paralyzed or frozen, start throwing the most effective Poké Balls according to the situation until it is caught.

Repel Trick
Repel Trick was a widely used tactic in core series games to find Roaming Pokémon. Repels, when used, shut down all Wild Pokémon encounters below the level of the player's leading Pokémon, so many players used this trick to track down Roaming Pokémon, which were almost guaranteed to be stronger than normal Wild Pokémon in those games. However, it is unfortunately disabled in Pokémon Brick Bronze for reasons currently unknown.

Regular Roaming Pokémon
All regular Roaming Pokémon have an encounter rate of 1/1000 (0.1%) and can be boosted by the game pass, as well as the Ro-Power. Their levels are always at Lv. 40. Once they show up, the music immediately changes to the Legendary and Mythical Pokémon battle theme when the screen flashes white.

Default Roaming Pokémon
These Pokémon can only be encountered as Roaming Pokémon. No Set Encounters are available for them. To trigger their Roaming encounters, players must first visit a certain location. Almost all of them roamed in core series Pokémon games as well, until Regigigas, which breaks this trend.

Roam After Set Encounters
The following Pokémon roam around Roria after battling in their Set Encounters, regardless of the result. Due to the extreme rarity, players should catch them during the Set Encounters rather than treating Roaming battles as second chances.

Event Roaming Pokémon
The following Pokémon roam around Roria during certain events. Their encounter rates are slightly higher than the afore-mentioned regular Roaming Pokémon, but they are still extremely rare to find. Their levels are also not fixed. Ro-Power and the game pass fail on these Pokémon. The background music will only be the normal Wild Pokémon battle theme when they appear.

Scale of Roaming Pokémon
Among all Regular Roaming Pokémon, within that 0.1% encounter rate, there is a hidden scale to determine how scarcely will a specific Roaming Pokémon show up. The scale runs from 2 to 4, with 2 being the lowest. A pattern can also be found in the scale, as follows:

MEW

Encountering Mew: Edit
Mew is a Legendary (Roaming) Psychic-Type Pokemon with the ability Synchronize. It can be found in Port Decca's Lab.

First, you will need a Pokemon that has learned the move Headbutt. After that, head to the lab that is right below Port Decca. You will see grey bins with oil under it. Click on it and use Headbutt, and you will watch a sequence where one of the workers gets angry because of the fallen oil bins. Proceed to walk up the stairs that has been blocked by him before, and search for a control panel with a green switch. Click on it and you will watch another sequence where a crane lifts up a red truck that unveils a basement pathaway to Mew. Enter it and you will have to battle 3 scientists before walking up to the capsule with Mew in it. Click on the machine and turn it off. Mew will use Teleport and you will be informed that it could now be found in the wild.

Scientist Jeremy - Porygon, Porygon2, Porygon Z

Scientist Albert - Magnemite, Magneton, Magnezone

Scientist Herald - Shinx, Luxio, Luxray

Trivia

 * The encounter rate of White Haunter was at first 1/800 (0.125%). A few days prior to the 2016 Halloween Event's end, the rate was increased to 1/500 (0.2%).